norwegian scabies = الجرب النرويجي · norwegian scabies = ﺐرﺠﻠا...

Norwegian scabies = النرويجي الجربSunday, 17 October 2010 16:55 - Last Updated Friday, 26 November 2010 12:49

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SCABIES Epidemiology Scabies is a human skin infestation caused by the penetration of the obligate human parasiticmite Sarcoptes scabiei var. hominis into the epidermis. The scabies mite is an arthropod of theorder Acarina which was first identified in the 1600s, but was not recognized as the cause of theskin eruption until the 1700s. There are estimates that over 300 million people worldwide areinfected with the scabies mite.2 Scabies affects all socioeconomic classes, with women andchildren being disproportionately infected. It tends to be more prevalent in urban areas,particularly in overcrowded regions. There is evidence of a seasonal variation, with more casesbeing diagnosed in the winter months than the summer. The incidence of scabies has beenincreasing over the past two decades, and has been found to be responsible for majoroutbreaks in nursing homes, prisons, and hospital wards. Transmission of the mite occursusually through close personal contact, although the scabies mite can live off the human skin forup to 3 days, and therefore some infections can be from exposure to fomites. Etiology and Pathogenesis The scabies mite has four pairs of legs and measures 0.3 mm in diameter. It is therefore noteasily seen with the naked eye. The mite cannot fly or jump; it lives its entire 30-day life cycle inand on the epidermis. The female mite burrows into the stratum corneum within 20 minutes andlays approximately 3 eggs a day. The eggs hatch after 4 days, and the larvae migrate to theskin surface and mature into adults.5 After 2 weeks, female and male mites copulate, afterwhich the gravid female burrows back into the stratum corneum. The male, which is slightlysmaller than the female, falls off the skin and perishes. The average number of mites a hostharbors is usually less than 20, except in “crusted scabies” (previously known as Norwegianscabies), in which a host may harbor over a million mites. 5Individuals with human immunodeficiency virus, the elderly, and patients withmedicationinduced immunosuppression are at risk of developing crusted scabies, although ithas been reported among immunocompetent indigenous Australians.6 Clinical Findings After the initial exposure to the scabies mite, the pruritus and rash may take up to 6 to 8 weeksto develop. Subsequent exposure to the mite results in the itching and the rash developingwithin a couple days, probably due to prior sensitization to the scabies mite.7 The itching issevere and usually worst at night. The lesions appear as red, scaly, sometimes crusted(excoriated) papules and nodules that favor the interdigital webs , sides of the fingers, volaraspects of the wrists and lateral palms , elbows, axillae, scrotum, penis , labia, and the areolae in women. A diffuse erythematous eruption on the trunk may bepresent and represents a hypersensitivity reaction to mite antigen. The pathognomonic lesion isa burrow, which is a thin, thread-like, linear structure that is 1 to 10 mm in length, and is atunnel caused by the movement of the mite in the stratum corneum. The burrow is best seen inthe interdigital webs, wrists, or elbows. However, it can be difficult to find in early cases of thecondition, or after the patient has extensively excoriated the lesions. Identification of a burrowcan be facilitated by rubbing a black felt-tip marker across an affected area. After the excess inkis wiped away with an alcohol pad, the burrow appears darker than the surrounding skin due toink accumulation in the burrow. In infants younger than the age of 2 years, the face and scalp can be infested, whereas inadults this is rarely the case. Erythematous to violaceous pruritic nodules found in the axillaeand flanks of the trunk are not an unusual finding in children and on the scrotum in men , andare thought to be a hypersensitivity reaction to the mite. These nodules can remain for manyweeks after the successful eradication of the mite infection. Vesicles and bullae may develop,particularly on the palms and fingers . In crusted scabies , hyperkeratotic plaques develop diffusely on the palmar and plantar regions,with thickening and dystrophy of the toenails and fingernails. The rest of the skin usuallyappears diffusely xerotic. Pruritus is variable and may be totally absent in this form of thedisease. Over a million mites populate the skin and these highly contagious patients can be thesource of outbreaks in health care facilities. The definitive diagnosis is made by the microscopic identification of the scabies mites, eggs, orfecal pellets (scybala). This is accomplished by placing a drop of mineral oil over a burrow andthen scraping longitudinally with a number 15 scalpel blade along the length of the burrow,being careful not to cause bleeding. The scrapings are then applied to a glass slide andexamined under low power (Fig. 208-5). Other diagnostic methods include dermoscopy (seeChap. 5) which can be used to examine the mite in vivo.10 A polymerase chain reaction-basedmethod has been described in which the DNA from the mite was detected from cutaneousscales. 11 A skin biopsy can bediagnostic, when the scabies mite is found transected in the stratum corneum . Differential Diagnosis Complications Secondary impetiginization is a common complication and usually responds well to eithertopical or oral antibiotics, depending upon the extent of the pyoderma. However, lymphangitisand septicemia can develop, particularly in crusted scabies . Post-streptococcalglomerulonephritis has resulted from scabies-induced pyodermas caused by Streptococcuspyogenes.12 Prognosis and Clinical Course If left untreated, the condition can persist for many years. In immunocompetent individuals, the number of mites may decrease over time. Treatment There are a number of treatments for scabies which have various levels of effectiveness.Factors which may determine which treatment to use are the age of the patient, the cost of themedication, the severity of the eruption, and if previous treatments have been unsuccessful. In adults, topical scabicides should be applied to the entire skin surface, excepting the face andscalp, with special attention to the intertriginous areas, the genitalia, the periungual regions, andbehind the ears. In children and those patients with crusted scabies, the face and scalp shouldalso be treated. Patients must be informed that even after adequate scabicidal therapy, the rashand pruritus may persist for up to 4 weeks; otherwise they may believe that the prescribedtreatment was unsuccessful, and then inappropriately overuse scabicidal medications. Topicalsteroids, antihistamines and, if necessary, a short course of systemic steroids, can beprescribed to alleviate the pruritus and rash once the patient has completed the scabicidetreatment.. Treatment for Scabies DRUG DOSE COMMENTS Permethrin 5% cream Applied for 8-14 h; often repeated in 7 days. First-line treatment in the United States; pregnancy category B Lindane 1% lotion Applied for 8 h then washed off. Second application recommended after 1 wk. Not recommended for children under 2, during pregnancy, or lactation; resistance has been increasing; banned in California Crotamiton 10% cream Applied on 2 consecutive days; repeated once within 5 days. Antipruritic qualities; may not be as effective as other topicals Precipitated sulfur 5%-10% Applied for 3 days and then washed off. Safe in children under 2 mo and during pregnancy, but messy to apply and limited efficacy data Benzyl benzoate 10% lotion Applied for 24 h then washed off. Not available in United States Ivermectin, 200 µg/kg Single oral dose, can be repeated in 10-14 days. Highly effective with a good safety profile; can be used along with topical agents, particularly in crusted or resistant cases Differential Diagnosis of Scabies Most Likely - · Atopic dermatitis - · Insect bite reactions - · Contact dermatitis - · Dermatitis herpetiformis - · Dyshidrotic eczema Consider - · Psoriasis, particularly in the crusted variety - · Bullous pemphigoid, when vesicles and bullae are present - · Drug eruption The only oral but highly effective scabicide known to date is ivermectin. It was discovered in the1970s in the fermentation broth of a soil actinomycete Streptomyces avermitilis. It is structurallysimilar to macrolidic antibiotics, but with no antibacterial activity.16 It is currently U.S. Food andDrug Administration (FDA) approved for the treatment of the intestinal stage of onchocerciasisand strongyloides, but not FDA approved for the treatment of scabies. Its activity against thescabies mite is due to its high affinity for the gluminatedgated chloride ions found in theperipheral nervous systems of invertebrates.17Ivermectin blocks the channel transmission across the nerve synapse that uses γ-aminobutyricacid. This results in the paralysis and death of invertebrate parasites. In mammals, thesereceptors are confined to the central nervous system and in normal conditions the drug does notcross the blood-brain barrier. It has been suggested that conditions that disrupt the blood-brainbarrier may allow the drug to enter the central nervous system.18Therefore the drug should not be used in children younger than the age of 5 years or weighingless than 15 kg, or during pregnancy or lactation, although there are reports of ivermectin beingused in young children and during pregnancy without adverse effects.19 There are been numerous reports of the effectiveness of ivermectin in the treatment in scabies.20The usual dosage is 200 µg/kg; often the dose is repeated in 10 to 14 days, but the optimaldosage schedule for the treatment of scabies has not been established. A clinical studycomparing ivermectin to topical 5 percent permethrin revealed that a single dose of ivermectinprovided a cure rate of 70 percent, which was increased to 95 percent with a second dose 2weeks later. A single application of permethrin was curative in nearly 98 percent of patients.21A topical preparation of 1 percent ivermectin has been shown to be effective in early clinicalstudies, but is not yet commercially available.22In crusted scabies, the combination of ivermectin and a topical anti-scabicide is often used dueto the severity of the infection, and multiple courses may need to be used to eliminate theinfection. Side effects of ivermectin are usually mild and transient; however, there have been reportedrare side effects of hypotension, laryngeal edema, and encephalopathy.23 There is one casereport of an increased death rate in elderly nursing home patients who were treated withivermectin. 24Subsequent studies have not confirmed this finding. Prevention Individuals in close contact with the infected person should be treated with a topical scabicide.Treatment should be directed to prevent spread of the scabies, because individuals may beharboring the scabies mite during the asymptomatic incubation period. Additionally, to preventre-infection with fomites, bed sheets, pillow cases, towels, and clothes worn during the past 5days should be washed and dried in the hot cycle, or be dry cleaned. Because the mite can live up to 3 days off of skin, carpets and upholstery shouldbe vacuumed. Pets do not need to be treated because they do not harbor the human scabiesmite.

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norwegian scabies = الجرب النرويجي · norwegian scabies = ﺐرﺠﻠا...

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